The present invention relates to a communication system in which a plurality of devices communicate via a network. More specifically, the present invention relates to a surveillance system that retrieves information from sensors and a surveillance camera via a network.
In an example of a communication system for a surveillance system of the type which is actually in use today, an operation unit and a plurality of monitors in a surveillance center are used to retrieve information from a plurality of surveillance cameras and sensors via a network. In this type of surveillance system, communications take place over a network between individual surveillance cameras and. individual monitors, or between a plurality of sensors and an operation unit. This allows information to be sent from the surveillance cameras and sensors to the monitors and operation unit.
In this context, technologies to allocate bandwidth are known. These technologies assign bandwidth (capacity) beforehand for use by an individual communication, thus allowing separate communications to be performed without obstructing each other. For example, in the technology disclosed in Japanese laid-open patent publication number 10-42280, the total bandwidth is divided up according to the types of information to be sent in the surveillance system, and each division is assigned an available bandwidth. When the surveillance system is operating, the surveillance cameras and sensors send information to the monitors and the operation unit within the bandwidth assigned to the type of information being sent.
Japanese laid-open patent publication number 6-284148 presents another bandwidth restriction technology for communication systems. In this technology, a device performs peer to peer audio/video communications. When the communication throughput increases, only audio communications take place. When the communication throughput is reduced, both audio and video communications take place.
In technologies such as the one disclosed in Japanese laid-open patent publication number 42280, bandwidth is assigned in a fixed manner according to the type of information, to transferred. The rate at which information is generated over time may not be uniform, such during the transfer of information indicating an abnormality from a sensor or of control data such, as response commands issued from an operation unit operated by a user. If bandwidth assignments are based on the maximum transfer rate, there will be many time intervals during which the assigned bandwidths are not being used efficiently.
On the other hand, assigning bandwidth based on the average information transfer rate for information that is generated in a non-uniform manner over time will prevent responsive transfer of information when more information is being generated. This is not desirable, since it will result in a delay in the collection of important information that must be transferred rapidly, such as information relating to the presence of an abnormality or response commands.
Rather than pre-assigning bandwidth based on the type of information to be transferred, it would also be possible to transfer information according to the rate at which the information is generated. For example, if a large amount of information is generated all at once, individual communications will be affected in unpredictable ways by other communications, thus allowing communication problems to take place. These problems can result in the loss of various information, such as information relating to abnormalities, or control data, such as response commands.
If, in these cases, the audio/video communication technology disclosed in Japanese laid-open patent publication number 6-284148 is used, there would still be delays in the collection of important information that must be transferred rapidly, such as information relating to abnormalities and response commands.
In a surveillance system handling communication of both information that is generated at a uniform rate over time and information that is not generated at a uniform rate over time, the object of the present invention is to provide efficient use of bandwidth without causing delays in important information that must be transferred quickly. Another object of the present invention is prevent delays and loss of communication of important information transferred over a network, such as in a surveillance system.
In order to achieve the objects of the present invention, the present invention can, for example, provide a surveillance system that performs data transfers over a network between input node for capturing the state of an object to be monitored, an output node for outputting information representing the state of the object to be monitored, and a control node for controlling the input node and the output node. The control node performs the following operations. Before transfer of a first type of data, which is to be transferred uniformly over time started, the control node assigns a transfer capacity or the transfer of the first type of data so that the total sum of the transfer capacities used for transferring the first type of data is no more than a prescribed amount that is smaller than the total transfer capacity of the network. For transfer is be transferred in a tin a second type of data, which is data that non-uniform manner over time, no transfer capacity is assigned. If the input node, the output node, or the control node performs the first type of data transfer, the data transfer rate corresponds to the transfer capacity assigned for the transfer. If the input node, the output node, or the control node performs the second type of data transfer, the data transfer rate corresponds to the available transfer capacity in the network.
With this kind of transfer system, the transfer of data that is to be transferred in a non-uniform manner over time is not pre-assigned a bandwidth (capacity). For the transfer of data that is to be transferred in a uniform manner over time, the total sum of the transfer capacities to be used for these data transfers is assigned to be no more than a prescribed amount that is smaller than the total transfer capacity of the network. Thus, capacity is always maintained for the transfer of data that is to be transferred in a non-uniform manner over time.
The probability that all the data generated in a non-uniform manner over time will reach a maximum simultaneously is statistically very small. Therefore, the transfer capacity maintained, as described above, can be smaller than the total maximum generation rate of all the data transfers. For example, if a statistically determined maximum of the total rate at which non-uniform data is generated is reserved as the transfer capacity, there will be almost no delays in the transfer of data generated non-uniformly over time. However, the allocated transfer capacity can be set to less than or greater than the total sum of the rates at which data is generated based on factors such as providing transfer capacity leeway and tolerability of delays in the surveillance system. Thus, with this surveillance system, bandwidth can be used more efficiently for data transfers compared to assigning bandwidth based on the maximum rates at which data is generated, and communication delays are prevented for important information that must be transferred quickly.
In order to achieve the objects of the present invention, the present invention can also provide a surveillance system that transfers data over a network between an input node capturing the state of an object to be monitored, and an output node for outputting information representing the state of the object to be monitored. This surveillance system includes the following means. The surveillance system according to the present invention includes controlling means for controlling an input node or an output node transferring a first type of data. If the network traffic increases to at least a prescribed level, the controlling means reduces the transfer rate of the transfer of the first type of data over the network. When the input node or the output node performing the transfer of the first type of data reduces the transfer rate in response to actions of the controlling means, a transfer rate for the second type of data that is different from that of the first type is maintained or increased. With this type of surveillance system, if the network traffic increases to at least a prescribed level, the transfer rate of the first data type being transferred over the network is reduced, thus allowing the transfer rate of the second data type to be maintained or increased. This prevents delays and data loss in the transfer of the second type of data.
In order to achieve the objects of the present invention, the present invention can also provide a network system including a communication node for engaging in communications belonging to one of a plurality of communication types via a network, and a control node connected to the network. The control node includes means for storing a conditions table containing conditions that the bandwidth usage in the network used by the different types of communications need to fulfill; means for detecting bandwidth usage for communications in the network, based on various communication types; means for controlling the communication node via the network so that when the bandwidth usage detected for each communication type does not fulfill the conditions contained in the conditions table, the bandwidth usage is changed to fulfill these conditions.
With this type of network system, the conditions table stored in storing means contains conditions for individual communication types. Conditions that are fulfilled based on relations with network bandwidth used by other communication types can be included. Appropriate conditions can be provided so that when the bandwidth usage for the second communication type exceeds the result of subtracting the bandwidth allocated to the first communication type, as indicated in the bandwidth information table, from the network bandwidth that can be used by the first communication type and the second communication type, then the bandwidth used for the first communication type can be reduced. Alternatively, if a communication of the second communications type is detected, a communication of the first communication type can be stopped. Thus, by using the second communication type for communication of important information, delays and data loss in important information can be prevented.